A majority of the loudspeakers manufactured and used today are of the electrodynamic type. A common design of an electrodynamic speaker includes a permanent magnet, a moveable coil within a magnetic field produced by the permanent magnet, and a membrane attached to the moveable coil. An alternating electric current flowing through the coil causes the coil to oscillate within the magnetic field, thus driving the membrane, which in turn produces a sound. An electrodynamic loudspeaker typically has a relatively large back volume behind the membrane, i.e., at a side of the membrane opposite to the side of the membrane from which the sound waves are propagated to the environment. The size of the back volume of an electrodynamic loudspeaker typically is reciprocally related to the intended frequency range of the loudspeakers, that is, a loudspeaker of a low frequency range typically has a relatively large back volume.
Notable alternatives to electrodynamic loudspeakers are piezoelectric loudspeakers and electrostatic loudspeakers.
Besides the underlying physical phenomenon that is used in a loudspeakers (electrodynamic, piezoelectric, electrostatic, etc.), loudspeakers may also be distinguished by their structure and their method of manufacture. In recent years various solutions were proposed that are aimed at manufacturing loudspeakers based on micromechanical constructions. Some of these solutions propose the use of piezoelectric or ferroelectric materials on micromechanical membranes made from silicon. For the manufacture of such micromechanical loudspeakers, a new material system is integrated into the semiconductor manufacturing process. Typically, the loudspeakers manufactured in this manner are analog transducers, as are the majority of today's loudspeakers.
In contrast to analog loudspeakers, digital loudspeakers use pressure waves having discrete sound pressure levels (SPL). To this end, the sound producing element within the digital loudspeaker performs a predefined movement of a predefined amplitude. A digital-to-analog conversion, which is typically performed electrically and upstream of an electrical input of an analog loudspeaker in many modern electronic devices, is actually moved to the sound or pressure variation side of a digital loudspeaker. The ear of a listener may also be involved in the digital-to-analog conversion of the digital sound signal. Digital loudspeakers typically comprise relatively large arrays of basic transducer elements.